adp3334's thermal pad

hi;

I made a stupid mistake. In one of my project I used a adp3334acp to regulate 7v input power to 6v output. according to the datasheet of adp3334, "the thermal pad is attached to the die substrate, so the thermal planes that the vias attach the package to must be electrically isolated or connected to VIN. Do NOT connect the thermal pad to ground."  But in my design, I carelessly attached the thermal pad to the ground. I thought this circuit will not work and I had to re-design it. But surprisingly, it did work! I got a 6V output from the 7V input.

My question is: should I follow the datasheet and connect the thermal pad to VIN or let it float? If I connect the thermal pad to ground, what will happen?

Attached is my circuit:

THX!

Donald

  • When we connect die to the thermal pad we use a material which is thermally conductive.  This comes in two variants - one is guaranteed to be electrically non conductive and the other is probably non conductive but not guaranteed.  When a product specifies that the pad needs isolated or connected to a particular supply then the latter material has been used.

    In many cases you will see no difference if you connect the pad to the wrong supply connection but in some of the parts, there will be an electrically conductive path between the substrate and the electrical ground.  When this happens you will see increased leakage and may get unusual behaviour and reliability issues.  Definitely should be avoided in the design!

  • Hi, Tim;

    Thanks for your rapid answer. So I was lucky!

    Donald